1. Field of the Invention
The present invention relates generally to a variable displacement type compressor that is employed to compress a refrigerant gas used in a vehicular air conditioning system. More specifically, the present invention relates to a swash plate type variable displacement compressor that can vary discharge displacement thereof by changing an inclination angle of a swash plate based upon the differential pressure between the suction chamber and the crank chamber.
2. Description of the Background Art
Conventionally, Japanese Unexamined Patent Publication No. 58-158382 discloses a swash plate type variable displacement compressor, which is a preferable compressor used in a vehicular air conditioning system. This compressor controls pressure in its crank chamber with respect to suction pressure in order to vary the discharge displacement of the compressor by varying an inclination angle of a swash plate in response to both suction and discharge pressures.
More specifically, according to this compressor, for example, when a cooling load decreases or a suction pressure decreases in response to a high speed rotation thereof, a bellows in a discharge displacement regulating mechanism is stretched because of the differential pressure balance between the suction pressure and atmospheric pressure. This stretch of the bellows causes a valve mechanism to be operated so as to decrease the capacity of a bleed passage between a suction chamber and a crank chamber. The gas passage disposed between the discharge chamber and the crank chamber is independently regulated by a separate valve mechanism. Therefore, the pressure in the crank chamber and the pressure acting on the rear surfaces of pistons is increased, causing the inclination angle of the swash plate to decrease. The stroke of each piston is thereby decreased, such that a preferable amount of refrigerant gas with respect to the suction pressure will be discharged.
However, according to the above-described conventional compressor, the highly pressurized refrigerant gas discharged from the discharge chamber after completing a compression stroke is used to increase the pressure in the crank chamber. When this refrigerant gas is supplied into the crank chamber through the gas passage or introduced into the suction chamber through the bleed passage, the pressure thereof is reduced. Therefore, there is a drawback that the power consumed to control the displacement is reduced by the amount relating to this reduced pressure.